Vascular diseases, such as atherosclerosis and the like, have become quite prevalent in the modern day. These diseases may manifest themselves in a number of ways, often requiring different forms or methods of treatment for curing the adverse effects of the diseases. For example, vascular diseases may take the form of deposits or growths in a patient's vasculature which may restrict, in the case of a partial occlusion, or, stop, in the case of a total occlusion, blood flow to a certain portion of the patient's body. This can be particularly serious if, for example, such an occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids.
To treat these diseases, a number of different therapies have been developed. For example, treatment devices have been developed that remove the material occluding a vascular lumen. Such treatment devices, sometimes referred to as atherectomy devices or ablation devices, use a variety of material removal means, such as rotating cutters or ablaters for example, to remove the occluding material. (The term "atherectomy device" as used in the specification refers to ablation devices for use in any portion of a patient's vasculature. Thus, while the atherectomy devices provided in accordance with preferred embodiments of the present invention are well suited for use in the coronary arteries, their use is not limited to the coronary arteries.) The material removal device, such as a rotatable burr, is typically rotated via a driveshaft that extends out of the vasculature of the patient and to an electric motor.
In operation, an ablation device is typically advanced over a guide wire placed in vivo until the material removal device is positioned just proximal to the occluded site. The motor is used to rotate the driveshaft and the material removal device, and the material removal device is moved through the occluded vessel. The material removal device removes the material from the vessel, rather than merely displacing or reforming the material as in a balloon angioplasty procedure.
Although such types of ablation devices provide desirable results, it is sometimes difficult to operate them strictly within preferred operating parameters. For example, it is desirable to only operate the material removal device while it is in contact with the lesion to be ablated. However, with conventional systems, once the ablation device works through a distal end of the lesion, the sudden lack of resistance causes the ablation device to dart forward. Such darting may result in unwanted ablation of a vessel wall, and is typically accompanied by an undesirably large rpm drop. More particularly, when in use, a material removal device, such as a rotatable burr, is spun at approximately 180,000 rpm. When the burr engages the lesion or unwanted deposits, the ablation process causes a drop of approximately 5,000 rpm. It is desirable to maintain a consistent rpm drop of approximately 5,000 during ablation of the lesion. If an excessive rpm drop occurs, it is typically accompanied by increased torque and an undesirable increase in heat, as well as an increase in quantity and size of particles generated by the ablation. Furthermore, if the ablation device darts forward far enough, it may engage a spring tip located at a distal end of a guide wire. The friction caused by the rotating ablation device may generate sufficient heat to weld the burr to the spring tip of the guide wire.
Given the considerations discussed above, it would be desirable to provide an ablation device that is easier to operate within selected parameters. The present invention fulfills this need, and provides further related advantages.